U.S. patent number 4,873,115 [Application Number 06/765,573] was granted by the patent office on 1989-10-10 for method of sythesizing carbon film and carbon particles in a vapor phase.
This patent grant is currently assigned to Toa Nenryo Kogyo K.K.. Invention is credited to Mitsuo Matsumura, Toshihiko Yoshida.
United States Patent |
4,873,115 |
Matsumura , et al. |
October 10, 1989 |
Method of sythesizing carbon film and carbon particles in a vapor
phase
Abstract
A vapor phase synthesis of carbon film and carbon particles
using a single or a mixed gas capable of supplying halogen,
hydrogen and carbon atoms is disclosed. Halogen radicals can
suppress the desorption of carbon atoms from the substrate, and the
carbon layer is obtained easily. Especially chlorine and fluorine
atoms are effective. An electron beam diffraction pattern
illustrated that diamond film can be obtained in this method.
Inventors: |
Matsumura; Mitsuo (Saitama,
JP), Yoshida; Toshihiko (Saitama, JP) |
Assignee: |
Toa Nenryo Kogyo K.K. (Tokyo,
JP)
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Family
ID: |
15294779 |
Appl.
No.: |
06/765,573 |
Filed: |
August 14, 1985 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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523249 |
Aug 15, 1983 |
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Foreign Application Priority Data
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Aug 13, 1982 [JP] |
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57-141559 |
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Current U.S.
Class: |
427/577;
427/573 |
Current CPC
Class: |
C23C
16/272 (20130101); C23C 16/277 (20130101) |
Current International
Class: |
C23C
16/27 (20060101); C23C 16/26 (20060101); B05D
003/06 () |
Field of
Search: |
;427/39,37,34,38,249,255
;423/458,445,446 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bell; Janyce
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Parent Case Text
This application is a continuation Ser. No. 06/523,249 filed filed
8/15/83 which is now abandoned.
Claims
What is claimed is:
1. A method of synthesizing a carbon film consisting essentially of
carbon and carbon particles consisting essentially of carbon on a
heated substrate in a vapor phase which comprises using a single
gas or a mixed gas capable of supplying halogen, hydrogen and
carbon atoms as a starting material and carrying out the process by
having the gas in a plasma state with the temperature of the
substrate being from about 100.degree. to 900.degree. C. and with
process being carried out under a pressure of from about 10 mm Torr
to several tens of Torr until said carbon film and carbon particles
deposit on the substrate while heated to about 100.degree. to
900.degree. C.
2. A method of synthesizing carbon film and carbon particles as set
forth in claim 1 wherein the halogen atom is a fluorine atom and/or
chlorine atom.
3. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 2, wherein the halogen atom is
fluorine atom.
4. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 1, wherein the starting gas is
diluted with a hydrogen and/or inert gas.
5. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 1, wherein the sum of the
hydrogen and the halogen contents in the carbon film and in carbon
particles formed is less than 15 atom %.
6. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 1, wherein the carbon film formed
is a diamond film.
7. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 1, wherein the carbon particles
formed are diamond particles.
8. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 5, wherein the carbon film formed
is a diamond film.
9. A method of synthesizing carbon film and carbon particles in a
vapor phase as set forth in claim 5, wherein the carbon particles
formed are diamond particles.
10. A method of synthesizing carbon film and carbon particles as
set forth in claim 3 wherein the starting material is a
fluorohydrocarbon.
11. A method of synthesizing carbon film and carbon particles as
set forth in any one of claims 3, 4, 1, 2 or 10 wherein the plasma
state is generated by means selected from the group consisting of
glow discharge, arc discharge and plasma jet methods.
12. A method of synthesizing a material selected from the group
consisting of a carbon film consisting essentially of carbon and
carbon particles consisting essentially of carbon on a heated
substrate in a vapor phase which comprises using a single gas or
mixed gas capable of supplying halogen, hydrogen and carbon atoms
as a starting material and carrying out the process by having the
gas in a plasma state with the temperature of the substrate being
from about 100.degree. to 900.degree. C. and with process being
carried out under a pressure of from about 10 mm Torr to several
tens of Torr until said material selected from the group consisting
of carbon film and carbon particles deposits on the substrate being
heated to about 100.degree. to 900.degree. C.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of synthesizing carbon film and
carbon particles by a vapor phase reaction.
2. Description of the Prior Art
Heretofore, diamond has been industrially applied to cutter and
cutting tools because of its high hardness. Recently, however, many
studies on the synthesis of diamond film have been carried out,
since the diamond has not only good thermal conductivity but also
has a possibility of preparing a semiconductor to provide a
heat-resistant electronic device.
It is known that diamond can be synthesized not only at a high
temperature under high pressure, but also its crystal can be grown
under low pressure by using a gaseous carbon compound (see, for
example, U.S. Pat. Nos. 3,030,187 and 3,030,188).
Only a diamond crystal smaller than that obtained in high pressure
method is obtained by the low pressure method, but the low pressure
method is attractive in the following reasons: firstly, it is
possible to synthesize a thin film which may be utilized as a
semiconductor; secondery, it is not difficult to introduce impurity
elements to get the semiconductor. Recently, an excellent method
using methane gas as a starting material was reported.
In order to obtain a carbon film as a semiconductor, however, it is
necessary to prevent unforeseen impurities from being incorporated
therein (the tendency is strong when the pressure is the reaction
chamber is high) and to control a film thickness carefully.
Therefore it is preferable to synthesize the carbon film in a lower
pressure. The pressure applied in the conventional method, however,
is in the range of several to several tens of Torr, then the
conventional method has a disadvantage in that it is impossible to
stably produce the film under a pressure lower than that specified
above.
We have made studies on carbon film expecting that a carbon film
having a uniform structure (just as hydrogenated amorphous silicon
has) can be satisfactorily utilized as a semiconductor material
even if the film does not have a perfect diamond structure.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide
a process for producing carbon film and carbon particles in which
the reaction is carried out in a mild condition to prevent
unforeseen impurities from being incorporated in the carbon
film.
A second object of the present invention is to provide a process
for producing carbon film and carbon particles in which the control
of the thickness of films can be easily made.
Thus, the present invention provides a method of synthesizing
carbon film and carbon particles characterized in that a single or
a mixed gas capable of supplying halogen, hydrogen, and carbon
atoms is used as a starting material.
According to present invention, it is possible to lower the
temperature of the substrate below that of the conventional method
when the vapor phase synthesis is carried out under a pressure
below several hundreds of mTorr. When the substrate temperature is
above 200.degree. C., it is not necessary to increase the pressure
in the reaction chamber above several hundreds of mTorr; this is
impossible in the conventional method. Thus, reaction conditions,
such as, the substrate temperature and the reaction pressure may be
varied over wide ranges.
The carbon film and the carbon particles produced in present
invention have basically a tetrahedral structure based on
carbon-to-carbon bonds, and hence they have a high hardness similar
to that of diamond and have excellent thermal properties. When they
are doped with an impurity, they can act as a semiconductor.
Therefore, they may be used in various purposes, such as abrasive
grain, edges of processing or cutting tools, coating agent,
heat-radiating plate of semiconductor element, and heat-resistant
semiconductor element.
When a vapor phase synthesis is carried out by using a gas capable
of supplying halogen, hydrogen, and carbon atoms as a starting
material, carbon film and carbon particles can be synthesized in a
very mild reaction condition, and the film thickness can be subtly
controled.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is the picture which illustrates the electron beam
diffraction pattern of carbon film obtained in this invention.
FIG. 2 illustrates the electron beam diffraction pattern of diamond
disclosed in prior work.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The "gas capable of supply halogen atoms" used in present invention
includes not only halogen molecules but also compounds which
contain halogen atoms in the molecular structure and have a vapor
pressure of above several Torr at ordinary temperature. Some of
these compounds include inorganic compounds such as halogenated
silanes as well as halogenated organic compounds.
The halogen atom in present invention can contribute to stabilize
the structure of carbon film and carbon particles by following
ways: since the halogen atom is very effective in forming ions or
radicals from hydrocarbons or from halogen containing compounds,
which are the source of carbon atoms, the reaction can be easily
occurred in a plasma atmosphere to produce carbon film and carbon
particles; the following surface growth reaction (which is occurred
during the growth of the carbon film and the carbon particles),
which is conected with bonding between halogen and hydrogen, is
very helpful in forming a tetrahedral structure based on the
carbon-to-carbon bonds of the carbon film and the carbon
particles,
wherein X is a halogen atom; the halogen atom can decrease the
dangling bonds in the carbon film and the carbon particles by
getting into them and bond with carbon atoms. Thus, halogen atoms
having smaller atomic radius and can form strong bond with a
hydrogen atom are preferable. The preferred halogen atoms are
fluorine and chlorine. Especially, fluorine is preferable for the
stable synthesis of the carbon film and the carbon particles under
low pressure. Thus, in present invention, the following molecules
are preferable as gases which can supply halogen atom: fluorine
molecule, fluorinated paraffinic hydrocarbons, fluorinated olefinic
hydrocarbons, fluorinated alycyclic hydrocarbons, fluorinated
aromatic hydrocarbons and fluorosilanes (SiHO.about.3 F4.about.1).
Among these compounds, C.sub.1 to C.sub.6 fluorohydrocarbons such
as fluoromethane, fluoroethane, trifluoromethane and
fluoroethylene, fluorocyclohexane and tetrafluorosilane are
particularly preferred.
The "gas capable of supplying hydrogen atoms" used in present
invention includes not only hydrogen but also compounds which have
a vapor pressure of above several Torr at ordinary temperature.
Some of these compounds include aliphatic hydrocarbons such as
methane, ethane and propane; aromatic hydrocarbons such as benzene
and naphthalene; unsaturated hydrocarbons such as ethylene and
propylene; ammonia, hydrazine and organic compounds having a hetero
atom.
The "gas capable of supplying carbon atoms" used in present
invention includes lower hydrocarbons, higher hydrocarbons having a
vapor pressure of above several Torr at ordinary temperature and
halogenated hydrocarbons.
In present invention, these gases may be used as a mixture. If
necessary, the mixed gas may be diluted with an inert gas such as
helium, neon or argon. When a gas containing halogen, hydrogen, and
carbon atoms in the same molecule (e.g., fluoroethane etc.) is
used, the gas may be used alone.
The vapor phase synthesis of present invention is carried out in
such a manner that the gas in a reaction chamber is brought into a
plasma state by electrical discharge or the like. In the
conventional method using methane as a starting material, it is
impossible to stably produce a carbon film, when the pressure in
the reaction chamber is as low as several hundreds of mTorr and the
temperature of a substrate is 250.degree. C. or higher, because the
desorption rate of the carbon atom from the surface of the
substrate is greater than the deposition rate; the desorption of
carbon atom is mainly caused by hydrogen in the reaction chamber.
In present invention, halogen and hydrogen atoms formed in the
vapor phase react with each other to form a hydrogen halide, then
an excess of activated hydrogen radicals present in the vapor phase
is reduced and the desorption rate of the carbon atom is
suppressed. Thus, the carbon film can be stably produced in present
invention. The suitable conditions of the vapor phase synthesis in
present invention is as follows: the present in the reaction
chamber is in the range of about 10 mTorr to several tens of Torr;
and the temperature of the substrate is about 200.degree. to
900.degree. C.
In present invention, the gas in the reaction chamber can be
brought into a plasma state by means such as high-frequency glow
discharge, low-frequency glow discharge, arc discharge, or plasma
jet method. The power density is about 0.4 to 3.0 W/cm.sup.2. Some
substrate, such as, glass plates, crystalline silicon or metallic
sheets may be used in present invention.
As a result, when a carbon film is produced by the method of
present invention, the structure of the carbon film is,
microscopically, a tetrahedral based on carbon-to-carbon bonds,
that is, a diamond structure, but macroscopically this structure is
disturbed to form so-called dangling bonds. But the structural
instability due to above disturbance can be moderated by make bonds
between hydrogen or halogen atoms and carbon atoms when halogen
atoms exist in the reaction chamber. Above reactions of the halogen
atom can prevent the formation of dangling bonds, and the entire
carbon film can be moderated into a diamond-like amorphous carbon
film.
EXAMPLES
The following examples are provided to illustrate present
invention, but are not to be construed as limiting the present
invention in any way.
EXAMPLE 1
A plasma CVD apparatus was used. A mixed gas of CH.sub.4 and
CF.sub.4 (about 1:4) at an overall flow rate of CH.sub.4 and
CF.sub.4 of about 10 SCCM (standard cubic centimeter) was
introduced into the reaction chamber. The reaction chamber was kept
under a pressure of about 100 mTorr, then discharged electrically
in a power density of about 3.0 W/cm.sup.2 to form a plasma state.
In this state, a carbon film was produced on the surface of a
silicon crystal substrate heated to about 350.degree. C. Electron
beam diffraction analysis (FIG. 1) showed that the carbon film had
a diffraction pattern of diamond (FIG. 2). Moreover, table 1
illustrate that plane distances calculated from FIG. 1 are same to
those of diamond. Elemental analysis by EPMA (electron probe
microanalysis) showed that no fluorine atom was present at all. The
C--H vibration mode was analysed by infrared spectroscopy to reveal
that about 6% of hydrogen atoms was present in the film.
TABLE 1 ______________________________________ Comparison of
observed interlayer spacings with reported values. Reported
Observed (ASTM 6-0675) d[A] I d[A] I/I.sub.1 hk1
______________________________________ 2.06 S 2.06 100 111 1.26 M
1.261 27 220 1.07 S 1.0754 16 311 0.88 M 0.8916 7 400 0.81 W 0.8182
15 331 ______________________________________
In table 1, I means the peak strength.
EXAMPLE 2
The procedure of Example 1 was repeated using quartz glass as a
substrate. Electron beam diffraction analysis showed that the
produced carbon film had a diffraction pattern of diamond shown
above.
EXAMPLE 3
A mixed gas of SiF.sub.4 and CH.sub.4 (9:1) diluted with argon gas
was used as a plasma discharge gas. The procedures of Examples 1
and 2 were repeated except that the pressure in the reaction
chamber was 200 mTorr, the power density was 0.6 W/cm.sup.2 and the
temperature of the substrate was 250.degree. C. A carbon film was
produced on the surface of each silicon crystal and quartz glass.
Electron beam diffraction analysis showed that the films had a
diffraction pattern of diamond. EPMA showed that neither silicon
nor fluorine atoms were present in the films at all. This fact may
suggest that SiF.sub.4 as a fluorine source was present in the form
of SiF2 in the plasma.
EXAMPLE FOR COMPARISON
The procedure of Example 1 was repeated except that single methane
gas was used in place of a mixed gas of CH.sub.4 and CF.sub.4. The
formation of carbon film was not found.
* * * * *